1. Field of the Invention
The present invention relates generally to building construction and reinforcement, and specifically to a continuity system that compensates for the downward settling of buildings caused by shrinkage of wooden members.
2. Description of the Related Art
A continuity system is a secondary support system that ties studs or other building elements together and resists lateral forces from events such as earthquakes or strong winds. Lateral forces tend to produce moment loads in the building, which can pull the building elements upward with respect to the building foundation. A continuity system resists such upward movement of the building elements. A continuity system generally comprises a plurality of spaced continuity lines (e.g., vertical rods) that provide a discrete structural mechanism or load path framework for the transfer of loads through the building to the structural elements that are intended to resist such forces, such as roof or floor diaphragms. For example, the presence of a continuity system might prevent a concrete wall panel from experiencing loads and/or moments that might damage the wall.
A known continuity system is described in U.S. Pat. No. 5,813,181 (“the '181 patent”), the entire disclosure of which is hereby incorporated herein by reference. The '181 patent describes a system in which a “continuity tie” or “hold-down” connection device (such as a Continuity Tie available from Trussed, Inc. of Perris, Calif.) comprises a member that defines a channel for receiving a threaded rod. In one application, the continuity tie is secured to a lateral surface of a vertical wooden stud of a building, and the rod extends through the continuity tie parallel to the stud. The rod may extend through a number of different continuity ties within one or several floors of the building. A lower portion of the rod is secured to a structural element below the stud (e.g., a floor or foundation). In one arrangement, the continuity tie has a horizontal end plate with an opening through which the rod extends, and a nut is threaded onto the rod just above the end plate. Since the rod and nut are substantially vertically fixed with respect to the structural element below, the nut and rod resist upward movement of the wooden stud and associated building elements relative to the structural building element, which is often caused by strong lateral forces on the building structure. This particular continuity system typically involves a plurality of continuity ties and rods secured to vertical studs throughout the building. Another known continuity system is described in U.S. Pat. No. 6,389,767 (“the '767 patent”), the entire disclosure of which is also hereby incorporated herein by reference, which describes a continuity system as part of a shear wall construction.
One problem with these particular continuity systems is that they do not accommodate shrinkage of the wooden members of the building. Wooden members often shrink over time due to the loss of moisture. In a typical building, there is often horizontal wooden flooring or other wooden members below a wall. As such horizontal wooden members shrink over time, the wall above moves down. The wall of course includes the vertical wooden members to which the continuity ties are secured, as well as the continuity ties that are bolted to such vertical wooden members. However, since the threaded rods are fixed with respect to, e.g., the building foundation, the continuity ties move downward with respect to the rods, such that the nuts no longer bear against the end plates of the continuity ties. This introduces some “slop” in the continuity system, which permits the wooden studs and associated building elements to move upward relative to the rods. Such slop often results in structural damage to the building when the building elements move upward, for example during an earthquake.